1. Field of the Invention
The present invention relates to a semiconductor device and fabricating method thereof. More particularly, the present invention relates to a complementary metal-oxide-semiconductor (CMOS) device and a metal-oxide-semiconductor (MOS) device and their fabricating methods therefore.
2. Description of the Related Art
In the development of integrated circuit devices, higher operating speed and a lower power consumption is often achieved by reducing the size of each device. However, further reduction in the dimension of each device is subjected to factors including the bottleneck in the fabricating technique and the expense in the production. Consequently, other types of techniques different from the technique of miniaturizing devices have been developed to improve the driving current of devices. With this background, somebody has proposed the utilization of the stress in the channel region of a transistor to combat the limits in device miniaturization. The method uses stress to change the pitch of silicon crystal grid so that the mobility of electrons and holes is increased and lead to a higher device performance.
One of the conventional method of utilizing stress to increase device performance includes using the stress in a silicon nitride layer that serves as a contact etching stop layer to influence the driving current of the device. Although the driving current in the n-channel region will increase when the tensile stress of the silicon nitride layer is increased, the driving current in the p-channel region will drop. Conversely, although the driving current in the p-channel will increase when the compressive stress of the silicon nitride layer is increased, the driving current of the n-channel region will drop. In other words, the method of using the stress in a silicon nitride layer to improve the performance of the transistor can be used only for increasing the driving current of a N-type metal-oxide-semiconductor (NMOS) transistor or the driving current of a P-type metal-oxide-semiconductor (PMOS) transistor. There is no way to increase the driving current of both the NMOS transistor and the PMOS transistor at the same time.
To increase the driving current of NMOS transistor and PMOS transistor simultaneously, a method for forming a semiconductor device with the following steps is proposed. First, an NMOS transistor and a PMOS transistor are formed on a substrate such that a shallow trench isolation (STI) structure is also formed between the two transistors. Hence, the NMOS transistor and the PMOS transistor are electrically isolated. Thereafter, a silicon nitride layer with tensile stress is deposited to cover up the entire substrate. After that, a patterned photoresist layer is formed over the silicon nitride layer with tensile stress to expose the silicon nitride layer above the PMOS transistor. Using the patterned photoresist layer as a mask, an etching process is performed to remove the exposed silicon nitride layer while retaining the silicon nitride layer on the NMOS transistor. Then, the patterned photoresist layer is removed. Afterwards, using a similar method, another silicon nitride layer with compressive stress is deposited over the entire substrate. Then, the silicon nitride layer above the NMOS transistor is removed while retaining the silicon nitride layer with compressive stress over the PMOS transistor. Consequently, a silicon nitride layer with tensile stress is formed over the NMOS transistor while another silicon nitride layer with compressive stress is formed over the PMOS transistor. In other words, the driving current of both the NMOS transistor and the PMOS transistor is increased simultaneously.
Although the aforesaid method can increase the driving current of both the NMOS transistor and the PMOS transistor, a few problems that may affect the driving current and performance of the transistors are not tackled. For example, in areas where the pitch between devices is small, the silicon nitride layer at different stress levels may merge together and doubling the thickness of the silicon nitride layer there. Therefore, the silicon nitride layer needs to be over-etched in an etching operation in order to ensure the silicon nitride layer not covered by the photoresist is completely removed. However, this extended etching may damage the film layers and elements such as the spacers and silicone dioxide layer and nickel-silicide of STI structure in the no-transistor region underneath the silicon nitride layer. Ultimately, there will be some adverse effects on the performance of the device.